(i) Technical Field
A certain aspect of the embodiments discussed herein is related to an amplifier.
(ii) Related Art
A Doherty amplifier is used as radio communications amplifier (see Japanese Patent Application Publication No. 2005-322993). The Doherty amplifier includes a carrier amplifier and a peaking amplifier. The carrier amplifier is an amplifier that primarily amplifies an input signal. The peaking amplifier is an amplifier that amplifies the peak of the input signal. For example, the carrier amplifier always amplifies the input signal. In contrast, the peaking amplifier amplifies the input signal only when the input signal has power equal to or higher than a predetermined level.
The Doherty amplifier includes an impedance transformer composed of, for example, a λ/4 phase line, an inductor and a capacitor. This kind of impedance transformer has a frequency dispersion characteristic for high frequency signals. This may result in a difference between the center frequency of the input signal and the center frequency of the amplifier and may decrease the drain efficiency.